The outage that began past noon Wednesday left 1.4 million customers without electricity and more than 400,000 without water. More than 742,600 customers, or 51%, had power back by Thursday morning, while 83% of customers had water restored. Officials expected 90% of customers to have power back within 48 to 72 hours after the outage.

“This is a shame for the people of Puerto Rico that we have a problem of this magnitude,” said Gov. Jenniffer González, who cut her weeklong vacation short and returned to Puerto Rico on Wednesday evening.

She said it would take at least three days to have preliminary information on what might have caused the blackout, which snarled traffic, forced hundreds of businesses to close and left those unable to afford generators scrambling to buy ice and candles.

“There’s still a long road of recovery,” she said. “Our system is very fragile.”

It’s the second island-wide blackout to hit Puerto Rico in less than four months, with the previous one occurring on New Year’s Eve.

Government under pressure to end contracts with energy firms

“Why on holidays?” griped José Luis Richardson, who did not have a generator and kept cool by splashing water on himself every couple of hours.

The roar of generators and smell of fumes filled the air as a growing number of Puerto Ricans renewed calls for the government to cancel the contracts with Luma Energy, which oversees the transmission and distribution of power, and Genera PR, which oversees generation.

González promised to heed those calls.

“That is not under doubt or question,” she said, but added that it’s not a quick process. “It is unacceptable that we have failures of this kind.”

González said a major outage like the one that occurred Wednesday leads to an estimated $230 million revenue loss daily.

Ramón C. Barquín III, president of the United Retail Center, a nonprofit that represents small- and medium-sized businesses, warned that ongoing outages would spook potential investors at a time when Puerto Rico urgently needs economic development.

“We cannot continue to repeat this cycle of blackouts without taking concrete measures to strengthen our energy infrastructure,” he said.

Many also were concerned about Puerto Rico’s elderly population, with the mayor of Canóvanas deploying brigades to visit the bedridden and those who depend on electronic medical equipment.

Meanwhile, the mayor of Vega Alta opened a center to provide power to those with lifesaving medical equipment.

What caused the blackout?

It was not immediately clear what caused the shutdown, the latest in a string of major blackouts on the island in recent years.

One possibility is that overgrown vegetation affected the grid, which, if true, should not have happened, said Josué Colón, the island’s energy czar and former executive director of Puerto Rico’s Electric Power Authority.

He noted that the authority flew daily to check on certain lines, something he said Luma should be doing.

Colón said Luma also needs to explain why all the generators shut down after there was a failure in the transmission system, when only one was supposed to go into protective mode.

Pedro Meléndez, a Luma engineer, said an investigation is ongoing. He said in a press conference Thursday that he did not immediately have details on when the company last did an air patrol, but said those occur with the frequency established in its contract.

Daniel Hernández, vice president of operations at Genera PR, said Wednesday that a disturbance hit the transmission system shortly after noon, a time when the grid is vulnerable because there are few machines regulating frequency at that hour.

Puerto Rico has struggled with chronic outages since September 2017, when Hurricane Maria pummeled the island as a powerful Category 4 storm, razing a power grid that crews are still struggling to rebuild.

The grid already had been deteriorating as a result of decades of a lack of maintenance and investment.